1. Field of the Disclosure
The present embodiments relate to an organic light emitting display device, and more particularly, to an organic light emitting display device and a method of driving the same, that prevent a sensing defect and increase an accuracy of external compensation, thus enhancing a display quality.
2. Discussion of Related Art
General organic light emitting display devices may include a display panel, which includes a plurality of pixels respectively formed in a plurality of pixel areas defined by intersections between a plurality of data lines and a plurality of gate lines, and a panel driver that causes light to emit from the plurality of pixels.
FIG. 1 is a circuit diagram for describing a pixel structure of a related art organic light emitting display device. With reference to FIG. 1, each pixel of the display panel may include a first switching TFT ST1, a second switching TFT ST2, a driving TFT DT, a capacitor Cst, and an organic light emitting diode OLED.
The first switching TFT ST1 may be turned on according to a scan signal (gate driving signal) supplied to a corresponding gate line GL. As the first switching TFT ST1 is turned on, a data voltage Vdata supplied to a corresponding data line DL may be supplied to the driving TFT DT.
The driving TFT DT may be turned on according to the data voltage Vdata supplied to the first switching TFT ST1. A data current I_oled flowing to the organic light emitting diode OLED may be controlled by a switching time of the driving TFT DT.
The capacitor Cst may be connected between a gate and source of the driving TFT DT. The capacitor Cst may store a voltage corresponding to the data voltage Vdata supplied to the gate of the driving TFT DT. The driving TFT DT may be turned on with the voltage stored in the capacitor Cst.
The organic light emitting diode OLED may be electrically connected between the source of the driving TFT DT and a cathode voltage VSS. The organic light emitting diode OLED may emit light according to the data current I_oled supplied from the driving TFT DT.
The related art organic light emitting display device may control a level of the data current I_oled flowing from a first driving voltage VDD terminal to the organic light emitting diode OLED by a switching time of the driving TFT DT based on the data voltage Vdata. Therefore, the organic light emitting diode OLED of each pixel emits light to thereby realize an image.
However, the threshold voltage (Vth) and mobility characteristics of the driving TFTs DT of the respective pixels may be different due to non-uniformity of the TFT manufacturing process. For this reason, in general organic light emitting display devices, despite that the same data voltage Vdata is applied to the driving TFTs DT of the respective pixels, a deviation of currents flowing in the respective organic light emitting diodes OLED occurs, causing the display device to have non-uniform image quality.
To solve the non-uniform image quality, a plurality of the sensing signal lines SL may be formed in the same direction as that of the gate lines GL, and a second switching TFT ST2 may be additionally formed in each pixel. The second switching TFT ST2 may be turned on according to a sensing signal applied to a corresponding sensing signal line SL. When the second switching TFT ST2 is turned on, the data current I_oled supplied to the organic light emitting diode OLED may be supplied to an analog-to-digital converter (ADC) of a data driver.
FIG. 2 is a diagram for describing a display and sensing driving method of a related art organic light emitting display device.
With reference to FIG. 2, in a driving mode where an image is displayed, data voltages Vdata corresponding to image data may be respectively supplied from the first data line to the last data line during a period of an Nth frame, thereby enabling an image to be displayed.
In a sensing mode, the display device may supply a sensing signal to one or some of all the sensing signal lines to perform real-time sensing during a blank interval between an nth frame and an n+1st frame. In a driving period where an image is displayed, a driving voltage Vref may be set as a display reference voltage Vpre_r. In a sensing period, the driving voltage Vref may be set as a sensing reference voltage Vpre_s.
The display device may supply a precharging voltage Vpre_s to all the pixels or some pixels to be sensed, and may selectively turn on the second switching TFTs ST2 of all the pixels or some pixels to detect a voltage charged into each of the corresponding sensing power lines RL. Subsequently, the display device may convert the detected voltage into compensation data corresponding to a threshold voltage/mobility of the driving TFT DT of a corresponding pixel P.
In such a scheme, the display device may detect the threshold voltage/mobility of the driving TFT DT of each pixel of the display panel during a blank interval of a plurality of frames. The display device may generate compensation data on the basis of the detected threshold voltage/mobility, and compensate for a data voltage Vdata applied to each pixel by using the compensation data.
Voltages of the reference power lines RL can respectively increase according to data voltages supplied in the driving mode. For example, a voltage of each of the reference power lines RL can increase by 0.5 V according to a white data voltage and a black data voltage.
In switching from the driving mode to the sensing mode, because a data voltage supplied in the driving period may not be sufficiently discharged, a voltage deviation of several tens of mV may occur between a plurality of sensing initial voltages. When a deviation of the sensing initial voltages occurs, a voltage deviation of several tens of mV may thereby occur between a plurality of sensing voltages, and for this reason, the accuracy of sensing for the external compensation is reduced.
FIG. 3 is a diagram for describing a problem in the related art of a non-uniform image quality caused by a sensing error.
With reference to FIG. 3, in switching from the driving mode to the sensing mode, sensing errors due to insufficient discharging can be continuously accumulated. In a state where the sensing errors are accumulated, when compensation of each pixel is performed, non-uniformity of the image quality can occur, causing a degradation of display quality. That is, in the driving mode, a deviation of sensing voltages may occur due to a pattern of an image displayed by the pixels, thereby causing a sensing error.
To solve such a problem, in switching from the driving mode to the sensing mode, the display device may wait until 100% discharge, and then sense each pixel. However, it can typically take several tens of milliseconds (for example, 30 ms to 50 ms) for discharging to be completed. This increase in discharging time causes the additional problem that the time available for sensing is shortened.